1. Field of the Invention
The present invention relates to techniques and devices for the decontamination and preservation of food products exposed to spoiling microorganisms and/or toxins. The invention more particularly relates to the use of ozone in the detoxification of agricultural products contaminated with mycotoxins.
2. Background of the Related Art
Mycotoxins are naturally occurring chemical compounds produced by certain species of fungi (e.g. Aspergillus sp., Fusarium sp., Penicillium sp.) which commonly grow on and infest plant materials such as grains, oilseeds and grasses. They are most often produced in the field under conditions of environmental stress on the plant (e.g. heat, insects, and drought). Aflatoxins are prevalent mycotoxins that present remarkable toxicity and hepatocarcinogenicity, that is, aflatoxins can cause diverse toxic effects on virtually all organs, eventually leading to the development of cancerous tumors capable of spreading throughout the entire body. There are four major aflatoxins (AfB.sub.1, AfB.sub.2, AfG.sub.1 and AfG.sub.2) that contaminate crops, with aflatoxins AfB.sub.1 and AfG.sub.1 having greater toxic potential than aflatoxins AfB.sub.2 and AfG.sub.2. The International Agency for Research on Cancer has particularly noted the major forms, AfB.sub.1 and AfG.sub.1, as potent carcinogens, linked primarily to cancer of the liver. Thus, the amount of aflatoxin allowed in human and animal food is regulated by state and federal agencies.
Fumonisin B.sub.1 is a mycotoxin that occurs almost exclusively on corn and can cause toxic effects in horses and swine. fumonisin B.sub.1 has been linked to esophageal cancer in humans and has been shown to be a cancer initiator and promoter in rodents. Tricothecenes (e.g. T-2 toxin, deoxynivalenol or `vomitoxin`), ergot, zearalenone, cyclopiazonic acid, patulin, ochratoxin A, and secalonic acid D are mycotoxins that can negatively impact human and animal health due to their diverse toxic effects. The toxic effects caused by these mycotoxins may be classified as acute or chronic, depending on the level and duration of mycotoxin exposure and species sensitivity.
Virtually all animals in the food chain can be affected by exposure to contaminated food and feed, including humans, who can be exposed directly to toxins through grain handling and consumption or indirectly through consumption of an unmetabolized parent compound or toxic metabolic products in contaminated meat or livestock products (e.g. milk and cheese.) As a result, mycotoxin contamination of agricultural commodities, such as corn, wheat, rye, rice, barley, oats, peanuts, pecans, soybeans, cottonseed, apples, grapes, alfalfa, clover, sorghum, and fescue grass forages, can result in severe economic loss at all levels of food production (e.g. cost of pre-harvest prevention, post-harvest treatment, down-grading, loss of contaminated grain, decreased animal productivity and increased loss of livestock, health care costs, etc.) Thus, a need has long been recognized for techniques, methods, and devices that would help reduce the levels of multiple mycotoxins in feeds for livestock and food for human consumption.
In U.S. Pat. No. 4,421,774, Vidal et al. disclose a method for preventing sprouting and mold and fungi proliferation in stored grain having moisture content in excess of 15%. The disclosed energy intensive methods of stored grain preservation include heating the grain and reducing the moisture content to below 15%. Treatment with 1% propionic acid has also been shown to prevent microbial growth, however, the color texture and taste of the grain may be affected and thus grain treated by the methods disclosed by Vidal et al. can only be used in the treatment of animal feed.
Vidal et al. also disclose a method wherein sulfur dioxide gas is bubbled through a propionic acid solution. The gas is used to transport the vapor pressure qualities of the acid to the grain mass. After a given period of time, the grain is perfused with ammonia gas. The process is designed to prevent the formation of A. flavus (a fungus) during storage, thus preventing the formation of mycotoxins. However, the process is not capable of removing aflatoxins that are present on the grains before being placed in storage.
In U.S. Pat. No. 4,035,518, Carmona et al. disclose a method particularly adapted for the treatment of nuts contaminated with aflatoxins. The nuts are placed in a 0.10% sodium hydroxide solution at a temperature of 212.degree. F. for 10 minutes. The nuts are then removed and washed in water until a neutral pH is attained. During this washing, the skins of the nuts are loosened by the sodium hydroxide and washed away allowing for color differentiation between the lightly colored uncontaminated peanuts and the deep dark contaminated peanuts. The color differences allow the contaminated and uncontaminated nuts to be sorted electronically. However, this process does not allow detoxification of the food contaminated with aflatoxins.
In U.S. Pat. No. 4,795,651, Henderson et al. use a flotation method to separate the contaminated grains or kernels. The authors describe methods that can be used to reduce the amount of aflatoxin contaminated material from feeds by physically removing them. The contaminated seeds rise to the top in a flotation medium while the uncontaminated seeds sink to the bottom. These processes present at least two drawbacks: 1) the high cost of removing and disposing of the contaminated materials in accordance with environmental guidelines, and 2) the difficulty of achieving complete removal of the contaminated kernels, seeds, etc. without wasting significant portions of the uncontaminated product.
Another method of removing mycotoxins is by altering them chemically by structural degradation following chemical treatment, or by physical absorption onto a reactive substrate. In U.S. Pat. No. 5,230,160, Gross et al. use microwaves and an applied vacuum to extract oil and moisture from seeds and nuts. The disclosed methods are designed as conventional continuous-type processes for the treatment of contaminated nuts. The contaminated food passes through a vacuum chamber where the microwaves are applied. The methods are based on the assumption that oil and water vapor fractions absorb the aflatoxins thus removing them from the food matrix. The water/oil/aflatoxin vapor is then condensed and removed. The aflatoxins can then be decontaminated before the mixture is discharged. One caveat presented by this technique is the need for extraordinary caution not to overheat the foods which necessitates that the microwave power be decreased incrementally along the chamber. Also, the heating process does not successfully destroy the aflatoxins (aflatoxins are relatively heat stable) nor does the treatment with microwaves.
In U.S. Pat. No. 5,165,946, Taylor et al. describe an inorganic animal food additive that chemically binds to and inactivates aflatoxins by combination in the gastrointestinal tract of the animal. A phyllosilicate clay is produced in pellet form and fed to livestock along with the mycotoxin contaminated meal. The aflatoxin binds to the clay during digestion and is excreted in the feces of the animal.
In U.S. Pat. No. 5,498,431, Lindner describes a method of detoxifying mycotoxins by an energy intensive process. Timed or untimed pulses of ultrasonic radiation are passed through an aqueous solution containing a suspension of grains or ground meal. In some cases, addition of alcohols, dilute acids and ammonia water to the aqueous suspension has been found to be somewhat beneficial. The radicals that are produced by the microcavition reaction attack the epoxide region of the various trichothecene mycotoxin molecules.
Treatment of grain with ammonia gas or ammonium hydroxide liquid has been found to reduce aflatoxin levels in corn, peanut meal, whole cottonseed and cottonseed products. Two procedures have been used in the ammoniation process: (1) High Temperature/High Pressure treatment, (HP/HT), and (2) Atmospheric Pressure/Ambient Temperature treatment, (AP/AT). HP/HT procedures involve the treatment of the contaminated product with anhydrous ammonia and water in a sealed vessel. The quantity of ammonia used in the treatment may vary between 0.5 and 2.0% while the moisture content is generally maintained between 12 and 16%. This treatment is maintained for up to one (1) hour at temperatures between 80 and 120.degree. C. and pressures around 50 psi. In the AP/AT process, a 13% ammonium hydroxide solution is sprayed onto the contaminated product as it is being packaged into a plastic silage bag. The bag is then sealed and held at ambient temperatures for between 14 and 42 days. The bag is generally probed and tested periodically for aflatoxin levels. Other methods of introducing ammonia to the contaminated products include using monomethylamine and lime in the HP/HT process or liberating ammonia using urea.
Ozone (O.sub.3) gas has been used for the sterilization and preservation of food and has recently been granted GRAS (Generally Recognized As Safe) status by the Food and Drug Administration.
Ozone is a highly reactive compound having a half life in air of only 24 hours. Ozone tends to react spontaneously and decompose according to the following reaction: EQU 2O.sub.3.fwdarw.3O.sub.2
Ozone's high reactivity introduces numerous problems. For example, ozone decomposition is easily accelerated by water, nearly all types of organic chemicals, and many types of inorganic chemicals. Ozone is also a surface active material, i.e. ozone decomposition is accelerated when ozone comes in contact with a surface, especially if the surface is organic in nature. Furthermore, ozone decomposition is accelerated at higher temperatures and pressures, by turbulence, ultrasound and ultraviolet light. Thus, unlike most conventional gases, ozone is not suitable for storage for more than a short period of time.
Where an ozone bearing gas is introduced into stored materials such as cereals, fruits, grasses, nuts and grains or other agricultural products, the ozone bearing gas may pass through the space between the grains of the material and displace air from the space around the material. Because of the generally organic nature of the stored materials and the high surface contact area of the grains, ozone may rapidly react and decompose into oxygen as it is being passed through this type of matrix. Therefore, it is generally difficult to maintain steady ozone concentrations in the interstices of the material to ensure adequate and uniform treatment of all the material in a storage container.
Ozone's high reactivity poses special problems when attempting to introduce and pass ozone though a porous organic medium such as agriculturally derived substances. In particular, special consideration must be given to controlling the dosing rate and achieving adequately high ozone concentrations uniformly throughout the entire stock of the stored material.
Uniform distribution of the ozone gas through the treated material may be complicated by multiple factors. For example, ozone reactivity may be so vigorous that when an ozone bearing gas is introduced into spaces around a material like grain or cereal, ozone may react immediately in the vicinity of the gas entry port resulting in excessive heating and accelerated ozone decomposition into oxygen in the immediate vicinity of the entry port. Furthermore, the ozone entry port may be overdosed with ozone, while grains located away from the entry port may have limited exposure to the ozone bearing gas. Furthermore, excess heating, which is more likely to occur at or near the entry port, may present significant hazard such as explosion of the container and/or fire.
Another important consideration in designing systems for detoxification by ozone treatment relates to the high cost of ozone generation. Decontamination by ozone treatment may only be cost effective if ozone waste is minimized.
In U.S. Pat. No. 3,341,280, Eolkin describes a method of using ozone and other gaseous compounds as a sterilizing gas for batch treatments of food. The chamber containing the food is evacuated, filled with sterilizing gas, and after a given period of time, the system is evacuated again to remove the sterilizing gas. However these systems present two major caveats: 1) heavy duty gauge material is always required in order to support the changes in pressure within the container and 2) almost unavoidable loss of the treatment gas to the atmosphere when the system is vented.
In U.S. Pat. No. 3,592,641, Rayner et al. describe a method of detoxifying aflatoxins in oilseed meals using ozone gas. Distilled water is added to ground meal to form a slurry with 22% to 30% water content. The mixture is then stirred and heated to a temperature between 75.degree. and 100.degree. C. and gassed with 25 mg/min O.sub.3 for 60 to 120 min. The ozonated slurry is spread in a thin layer and air dried for 48 hours. While the technique allowed some decrease in aflatoxin contamination, its effective implementation in enhancing the nutritional and toxicological qualities of the ozonated meal is drastically limited by the necessity to heat the mixture, which dramatically increases the rate of decomposition of ozone into molecular oxygen prior to ozone's reaction with the aflatoxin molecule.
In U.S. Pat. No. 4,549,477, McCabe describes the use of ozone in a continuous treatment ozone based process for the preservation of food products. The food products are conveyed along an elongated housing structure filled with ozone on a series of conveyor units. Ozone gas is distributed at spaced locations along the conveyor belt so that ozone may continually displace air or oxygen present in the chamber. Because ozone is denser than both air and oxygen it acts as a blanket with limited diffusion away from the food. The disclosed system suffers several limitations including the need for the storage of large quantities of ozone, as well the potential for ozone waste and release into the atmosphere.
In U.S. Pat. No. 5,011,699, Mitsuda et al. disclose a method wherein ozone gas is mixed with an inert gas such as carbon dioxide or nitrogen to act as food sterilizer. The carbon dioxide gas may help the ozone penetrate inside the food stuff being treated, and nitrogen gas may help prevent the food stuff from changing color and from emitting offensive odors associated with excessive oxidation. The disclosed technique, however, suffers from the same limitations as the ozone treatment systems discussed above, and does not provide for controlled supply and release of the ozone.
In U.S. Pat. No. 5,403,602, Endico uses ozonated water to act as an oxidizing agent in the treatment of food with ozone. An oxygen sensor is used to monitor the increase in oxygen gas resulting from the decomposition of the ozone.
Thus, there is a need for ozone treatment systems, methods or devices that would partially or totally eliminate the need for storing ozone prior to its use in treating contaminated materials. It would also be desirable to provide improved systems of the introducing and distributing ozone through the contaminated material so that the contaminated material is uniformly exposed to the ozone. Furthermore, it would be desirable if the system prevented overheating and pressure buildup, made optimum use of ozone, and reduced or eliminated ozone waste and transfer to the environment. More particularly, it would be desirable to have a system that would provide better ozone treatment of dry contaminated material.